If the focal point when an electron beam in an X-ray tube which is an X-ray generating source hits a target is not restricted to an appropriate level at the time of performing nondestructive inspection using an X-ray inspection apparatus, a penumbra is formed in a an imaging area, blurring the image. Even if the focus lens in the X-ray tube (open tube) is initially adjusted so that the focal point is restricted to an appropriate level, the focal point may become wider as the position of the filament or the target is deviated at the time the filament or the target is replaced. The focal point may also become wider when the tube voltage to be applied to the target of the X-ray tube is changed. As a measure in such a case, conventionally, a customer engineer has adjusted the focus lens in such a way that an image appearing on the monitor of the X-ray inspection apparatus becomes absolutely clear.